[slurm-users] Problem with sbatch

Daniel Torregrosa daniel.torregrosa at insight-centre.org
Tue Jul 9 14:53:37 UTC 2019

Thanks a lot for your answers again!

@Marcus Thanks a lot for the clarification.

About --uid, you are correct, I was mistyping it as -uid. But, the
behaviour is slightly inconsistent:
* If correctly typed (--uid) sbatch properly complains about needing to be
* If not present at all, or ignored (by adding a non-commented line before,
like you said), everything goes fine
* If incorrectly typed (-uid UID), it silently fails UNLESS /home/UID/d
exists, then it is run as the requested user, i.e. if I add

#SBATCH -uid test2

the log complains about /home/test2/d not existing. After creating that
file as test2 (that is, the file /home/test2/d is -rw-r--r-- test2:test2),
it executes the task as test (i.e. the output is, by default, in /home/test
and owned by test). I guess this is a bug?

@Jeffrey Sorry, slurmdUser=sudo was a typo. Thanks a lot for the
clarifications regarding the POSIX capabilities.

On Tue, 9 Jul 2019 at 14:49, Jeffrey Frey <frey at udel.edu> wrote:

> > So, if I understand this correctly, for some reason, `srun` does not
> need root privileges on the computation node side, but `sbatch` does when
> scheduling. I was afraid doing so would mean users could do things such as
> apt install and such, but it does not seem the case.
> The critical part here is slurmstepd running as one user (root, or slurm
> in your case) attempting to seteuid/setegid/setreuid/setregid the process.
> If not running as root, you'll see in the slurmstepd source code that the
> seteuid/setegid/setreuid/setregid calls are skipped -- thus, all job tasks
> run as SlurmdUser.  On a multiuser system, SlurmdUser=root is necessary and
> safe.
> > I am not going to be managing the actual cluster, only exploring
> possibilities. At this point I am mostly convinced slurmdUser=sudo is safe,
> so that is one less potential problem.
> SlurmdUser must be set to a user name present on the machine.  Setting it
> to "sudo" merely has it run as a user named "sudo."
> > @Patrick: I do not know how to do that. I only know that I can make
> slurm sudoer and NOPASSWD, but slurm would still call to `chown` (not `sudo
> chown`). An alternative would be replacing `chown` with a small script that
> calls `sudo chown`, but that is likely to break a lot of stuff. I assume
> slurmd will also need other root-only commands to work.
> The chown in question is a chown() system call in the slurmd/slurmstepd
> source code that's compiled into slurmd/slurmstepd.  Replacing
> /usr/bin/chown with a custom command that calls sudo would not help at all
> (and would probably create a security issue).
> > @Michael Indeed, the documentation/tutorials often mention that
> SlurmdUser should be root, but it is not clearly explained why anywhere
> (e.g. https://slurm.schedmd.com/quickstart_admin.html section Daemons).
> It seems that `srun whoami` returns the current user (and not root), so
> even when slurmdUser is root, users do not have privileges, so in principle
> there is no problem at all.
> Again, the critical part here is slurmstepd's having the ability to change
> the running uid/gid of the processes it starts.  With SlurmdUser=root, it
> can do this.  With any other user name, it cannot, and every job step runs
> as SlurmdUser.
> > @Jeffrey It is expected to be multi-user. As for your third option, I
> think you refer to something similar to what I wrote for Patrick.
> I was talking about POSIX capabilities, and the possibility that all the
> capabilities exist to grant to slurmstepd the ability to chown() like root
> can, etc.  That still doesn't help with the
> seteuid/setegid/setreuid/setregid calls because slurmstepd doesn't even
> make those calls when it's not running as root.
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::
> Jeffrey T. Frey, Ph.D.
> Systems Programmer V / HPC Management
> Network & Systems Services / College of Engineering
> University of Delaware, Newark DE  19716
> Office: (302) 831-6034  Mobile: (302) 419-4976
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::
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